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(p200300d82f42da00badfcc5523d51679.dip0.t-ipconnect.de. [2003:d8:2f42:da00:badf:cc55:23d5:1679]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-459c58ed0ecsm81898565e9.4.2025.08.06.13.14.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 06 Aug 2025 13:14:41 -0700 (PDT) Message-ID: <055a8a69-731d-43b8-887e-54d8718877cb@redhat.com> Date: Wed, 6 Aug 2025 22:14:39 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v2] mm/zswap: store Cc: SeongJae Park , "Liam R. Howlett" , Andrew Morton , Chengming Zhou , Johannes Weiner , Jonathan Corbet , Lorenzo Stoakes , Michal Hocko , Mike Rapoport , Suren Baghdasaryan , Vlastimil Babka , Yosry Ahmed , kernel-team@meta.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Takero Funaki References: <20250805002954.1496-1-sj@kernel.org> <761a2899-6fd9-4bfe-aeaf-23bce0baa0f1@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAmgsLPQFCRvGjuMACgkQTd4Q 9wD/g1o0bxAAqYC7gTyGj5rZwvy1VesF6YoQncH0yI79lvXUYOX+Nngko4v4dTlOQvrd/vhb 02e9FtpA1CxgwdgIPFKIuXvdSyXAp0xXuIuRPQYbgNriQFkaBlHe9mSf8O09J3SCVa/5ezKM OLW/OONSV/Fr2VI1wxAYj3/Rb+U6rpzqIQ3Uh/5Rjmla6pTl7Z9/o1zKlVOX1SxVGSrlXhqt kwdbjdj/csSzoAbUF/duDuhyEl11/xStm/lBMzVuf3ZhV5SSgLAflLBo4l6mR5RolpPv5wad GpYS/hm7HsmEA0PBAPNb5DvZQ7vNaX23FlgylSXyv72UVsObHsu6pT4sfoxvJ5nJxvzGi69U s1uryvlAfS6E+D5ULrV35taTwSpcBAh0/RqRbV0mTc57vvAoXofBDcs3Z30IReFS34QSpjvl Hxbe7itHGuuhEVM1qmq2U72ezOQ7MzADbwCtn+yGeISQqeFn9QMAZVAkXsc9Wp0SW/WQKb76 FkSRalBZcc2vXM0VqhFVzTb6iNqYXqVKyuPKwhBunhTt6XnIfhpRgqveCPNIasSX05VQR6/a OBHZX3seTikp7A1z9iZIsdtJxB88dGkpeMj6qJ5RLzUsPUVPodEcz1B5aTEbYK6428H8MeLq NFPwmknOlDzQNC6RND8Ez7YEhzqvw7263MojcmmPcLelYbfOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCaCwtJQUJG8aPFAAKCRBN3hD3AP+DWlDnD/4k2TW+HyOOOePVm23F5HOhNNd7nNv3 Vq2cLcW1DteHUdxMO0X+zqrKDHI5hgnE/E2QH9jyV8mB8l/ndElobciaJcbl1cM43vVzPIWn 01vW62oxUNtEvzLLxGLPTrnMxWdZgxr7ACCWKUnMGE2E8eca0cT2pnIJoQRz242xqe/nYxBB /BAK+dsxHIfcQzl88G83oaO7vb7s/cWMYRKOg+WIgp0MJ8DO2IU5JmUtyJB+V3YzzM4cMic3 bNn8nHjTWw/9+QQ5vg3TXHZ5XMu9mtfw2La3bHJ6AybL0DvEkdGxk6YHqJVEukciLMWDWqQQ RtbBhqcprgUxipNvdn9KwNpGciM+hNtM9kf9gt0fjv79l/FiSw6KbCPX9b636GzgNy0Ev2UV m00EtcpRXXMlEpbP4V947ufWVK2Mz7RFUfU4+ETDd1scMQDHzrXItryHLZWhopPI4Z+ps0rB CQHfSpl+wG4XbJJu1D8/Ww3FsO42TMFrNr2/cmqwuUZ0a0uxrpkNYrsGjkEu7a+9MheyTzcm vyU2knz5/stkTN2LKz5REqOe24oRnypjpAfaoxRYXs+F8wml519InWlwCra49IUSxD1hXPxO WBe5lqcozu9LpNDH/brVSzHCSb7vjNGvvSVESDuoiHK8gNlf0v+epy5WYd7CGAgODPvDShGN g3eXuA== Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: LLvDLJwgY6lbGyQc4OanS8FJjoLw3mW8Dhl70Uc2lYA_1754511283 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: BA56A18000C X-Stat-Signature: ax7xbnhsd53cf66e4r8x6b8zgs8nuszs X-HE-Tag: 1754511285-679512 X-HE-Meta: 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 e8Tl2yfs 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 05.08.25 18:56, Nhat Pham wrote: > On Tue, Aug 5, 2025 at 3:47 AM David Hildenbrand wrote: >> >> On 05.08.25 02:29, SeongJae Park wrote: >>> When zswap writeback is enabled and it fails compressing a given page, >>> the page is swapped out to the backing swap device. This behavior >>> breaks the zswap's writeback LRU order, and hence users can experience >>> unexpected latency spikes. If the page is compressed without failure, >>> but results in a size of PAGE_SIZE, the LRU order is kept, but the >>> decompression overhead for loading the page back on the later access is >>> unnecessary. >>> >>> Keep the LRU order and optimize unnecessary decompression overheads in >>> the cases, by storing the original content in zpool as-is. >> >> Does this have any effect on the movability of the given page? IOW, does >> page migration etc. still work when we store an ordinary page of an >> shmem/anon folio here? > > Good question. This depends on the backend allocator of zswap, but the > only backend allocator remaining (zsmalloc) does implement page > migration. Right, but migration of these pages works completely different than folio migration. But I think the part I was missing: we are still performing a copy to another page, it's just that we don't perform any compression. So I guess *breaking* movability of folios is not a concern. But yeah, whether these "as is" pages are movable or not is a good question as well -- in particular when zsmalloc supports page migration and the "as is" pages would not. Maybe someone familiar with the code could shed a light on that. -- Cheers, David / dhildenb